how can i populate a dropdown list and textboxes with matched strings?

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Javascript

How can I populate a dropdown list and textbox with the matched strings? I have an array consisting for few characters and a normal string.
I have used the following but how can I use the matched strings to populate textboxes?

Here is the code which I have used:

var populatedata = document.getElementById("<%=txtparse.ClientID %>").value;
  var newdata = new Array();
  newdata = populatedata.split('when');
  for (var i = 0; i < newdata.length; i++) {
      var sign = ["AND", "<", ">", ">=", "<=", "then",' '];
      for (var j = 0; j <= sign.length; j++) {
          var match = newdata[i].match(sign[j]);

txtparse is the ASP.net ID of the textbox which contains the string. Taking the string from this textbox based on matching strings with sign array I have to populate textbox.
:confused: :sigh:

Kindly help me out.